perf c2c: Fix c2c report for empty numa node

Ravi Bangoria reported that we fail with an empty NUMA node with the
following message:

$ lscpu
NUMA node0 CPU(s):
NUMA node1 CPU(s): 0-4

$ sudo ./perf c2c report
node/cpu topology bugFailed setup nodes

Fix this by detecting the empty node and keeping its CPU set empty.

Reported-by: Nageswara R Sastry <[e-mail]>
Signed-off-by: Jiri Olsa <[e-mail]>
Tested-by: Ravi Bangoria <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Jonas Rabenstein <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-c2c.c

···
 		if (!set)
 			return -ENOMEM;
 
+		nodes[node] = set;
+
+		/* empty node, skip */
+		if (cpu_map__empty(map))
+			continue;
+
 		for (cpu = 0; cpu < map->nr; cpu++) {
 			set_bit(map->map[cpu], set);
 
···
 
 			cpu2node[map->map[cpu]] = node;
 		}
-
-		nodes[node] = set;
 	}
 
 	setup_nodes_header();